How An Automotive Relay Works and How to Wire 'Em up

this is a relay a very common component modern automobiles use them for a lot of different things whole intent behind a relay is to allow us to turn on and off a circuit that has a high current load with a smaller current so we'll use a small amount of amperage to control a circuit that requires a lot of amperage the reason we want to do that is because high amperage circuits would require real heavy-duty switches which would be difficult to integrate into the interior of a modern car that's why we use relays now relays are very very common in circuits where we have things like electric fuel pumps power windows electric water pumps electric fans we use them in aftermarket applications for nitrous solenoids and things like that so they're all over the place and cars trucks so this relay is a pretty good representation of a Bosch style v terminal relay it's rated to 30 amps and that means that this can control a current up to 30 amps beyond 30 amps and you would have to get a relay that could handle more current let's look real quickly at this relay you'll notice on the bottom and I know it's kind of hard to see but each one of these terminals on the bottom has a number this is 86 30 85 87 and the center terminal is 87 a that's important because the terminal numbers tell us how this relay should be wired so the other thing you'll see on a lot of relays is there's a diagram on the side and this one's difficult to see this diagram will give us a pretty good idea again how these circuits are supposed to go together and how they're supposed to work let's draw this out all right let's begin by looking at each one of the terminals and I'm going to put terminal number 86 terminal number 85 separate over here terminal 37 or 38 e7 a an 87 now there's a reason why I separated those out a little bit this section of the relay on this side so from here over this is our control side what that means is that whatever circuit I'm going to use to control the load is going to be operated off of these two terminals 86 and 85 all right 86 could be our voltage source terminal and we can have a switch either on the power side or the ground side it doesn't matter in the relay itself we have an inductor and then next to the inductor is a resistor the resistor and diode here allows this thing to be directional when I talk about an inductor what I'm really saying is I have a coil of wire so this coil of wire right here is connected to terminals 86 and 85 what happens is when I put current into 86 and out 85 then I create a magnetic field around this coil of wire and when I create this magnetic field what that does is pulls this contact from the normally open position so it will close position so what that is that's a switch that's all that is is just a switch so when we energize this thing and create this current right here magnetic field switch comes over this position and now I'm going to turn things on that brings us to this side of the relay pin 3087 a and 87 for this style relay the normal position so no current flowing flowing through 86 and 85 is from 3287 I have voltage in and then here I could put a load on 87 a if I wanted that's generally not what you see generally what we have is our load over here at pin 87 so now I can draw this line here I've got my load whatever it may be maybe it's a nitrous solenoid electric water pump electric fuel pump whatever when I bring current through 86 and through 85 then what happens is my switch goes from 30 to 87 and I now allow current to go from here to here into my load so let's take a quick look at how that actually works they've got a motor right here and I'm going to wire this motor up first thing I want to do is I want to go ahead and set up a switch to this battery so I'll find some jumper wires here that'll allow me to do that alright switch in and then I need to go from the switch to my relay and we'll just use this relay right here so from here to this relay and I want to go to pin 86 which in this case is right there from pin 86 I'm going to go through the coil and back out pin 85 so I need to take pin 85 here back over to ground so there's the relay now hooked up to the switch in the battery now I need to set the load up I need to get this motor set up so I'm going to go ahead and take power again from the battery and since I'm going into a pretty heavy load I am going to fuse this circuit it's just a 10 amp fuse but it'll be plenty for the short period of time that this thing is going to run assuming I can took all this crap up all right now the load I need my power to the load coming in on pin 30 which is this pin right here so I'm going to hook that up to 30 okay then like I said with this particular relay the normal position has continuity between pin 30 and pin 87 a well I need this thing to operate not all the time but when I turn it on with the switch so I need to hook the load itself up to pin 87 so we'll take a jumper wire go to pin 87 and then just hook that motor up to the Y you're going to pin 87 and then I'm going to take another jumper wire and put the motor back to ground so jumper wire there and connect it to the battery all right so now there's my circuit and it's kind of ugly but it'll work so if everything is working properly when I turn the switch on we should see this switch right here engage and when it does the motor should run right now I'm just doing that by hand watch the motor see I can just do that by hand but that's not very convenient for us when we're driving down the road so we use a switch there we go all right switch on and then this switch is rotating over and the motor runs so do that again see the switch in the relay move motor run okay everything seems to be working normally that's pretty much how we're going to set up a relay now there may be some situations where you may want to put maybe a light bulb or something like that off of Terminal 87 a really the only reason you would do that would be if you had a situation where maybe you wanted to have a light on to tell you that something was going to be you know off and then the light would go off when it was on I don't know but it could be done now you can see I'm hooked up to 87a and the bulb is operating even though our switch here is in the off position so the switch off means that the relays not energized and the bulbs operating but when I energize the relay again let's leave that switch the in relay the bulb should go off and the motor should run exactly what's going on bowled off motor runs switch in the relay engages alright so I know this is a pretty nasty looking mess of wires it looks confused but really when you start wiring these things up they're really pretty simple and they're extremely useful so relays again they're all over the place and modern vehicles and knowing how to hook them up set them up and do it properly is pretty important for anybody working on cars these days

Channel: 2ton220

Views: 2,193,038

Rating: 4.831563 out of 5

Keywords: Relays, automotive, how to, automotive electrical, electrical systems, Cars, Automotive Industry (Industry), Street, trucks, race cars, hot rod

Id: UAeKTlieYhw

Length: 10min 50sec (650 seconds)

Published: Sun Dec 01 2013